Tidings pigeons bring

RESEARCH

Tidings pigeons bring

A group of scientists at the University of Utah has decoded the genetic blueprint of the rock pigeon species, unlocking secrets about pigeons’ Middle East origins and feral pigeons’ kinship with escaped racing birds. The study also throws light on how mutations give pigeons traits like a fancy feather hairdo, known as the head crest, reports Kalyan Ray.

Charles Darwin was a pigeon afficionado. Not only did he love them, but also relied heavily on the dramatic results of artificial selection in pigeon breeding to communicate his theory on natural selection to the wider audience.

In his ‘Origin of Species’, Darwin noted that pigeon breeds were so distinct that, based on morphology alone, a taxonomist might be tempted to classify them as completely different genera. Yet he also concluded that all breeds were simply variants within a single species, the rock pigeon Columba livia.

More than two centuries later, a group of scientists at the University of Utah decoded the genetic blueprint of this rock pigeon species, unlocking secrets about pigeons’ Middle East origins, feral pigeons’ kinship with escaped racing birds, and how mutations give pigeons traits like a fancy feather hairdo, known as the head crest.

“Birds are a huge part of life on earth, and we know surprisingly little about their genetics,” says Michael Shapiro, one of the two principal authors of the study on the genome sequencing that appeared in February 1 issue of Science. “There are more than 10,000 species of birds, yet we know very little about what makes them so diverse genetically and developmentally.”

Pigeons were probably domesticated in the Mediterranean region at least 3,000–5,000 years ago. Their remarkable diversity can be viewed as the outcome of a massive selection experiment by breeders in Europe. Darwin classified 32 breeds into four groups based on their morphology. They are: the pouters and croppers, which have enlarged crops; wattle breeds many of which have elaborated beaks and large-bodied runts; an artificial grouping diagnosed by a relatively short beak; and breeds that resemble the ancestral rock pigeon. But there are now 350 odd breeds with different sizes, shapes, colours, patterns, beaks, bone structure, vocalisations, flight arrangements and arrangements of feathers on the feet and head, including head crests that come in hoods, manes, shells and peaks.

Earlier studies and pigeon origins

A 2012 study by Shapiro provided limited evidence of pigeons’ origins in the Middle East and some breed origins to India. It also indicated kinship between common feral or free-living city pigeons and escaped racing pigeons.

Modern breeds are frequently described as having origins in England, Germany, Belgium, or elsewhere in Europe, but their progenitors were probably brought there from afar by traders or colonialists.

Most historical accounts trace the origins of the wattle breeds, owls, and tumblers to the Middle and Near East hundreds of years ago, with ancient breeds transported to Europe and India for further development by hybridisation or selection. The genetic analyses are consistent with the common geographic origin.

The fantail breeds probably originated in India and underwent less outcrossing than many other breeds. They show surprising affinity with pouters. These two groups are among the most morphologically extreme of all domestic pigeons, and among the most different from each other. European breeders developed pouters for several hundred years after these birds were brought to Europe from India by Dutch traders.

Historical accounts and genetic similarity between fantails and pouters support the theory of common geographic origin in India. Domestic rock pigeons, on the other hand, were first brought to North America approximately 400 years ago. “Few breeds that are typically associated with India, including the fantails, are genetically very similar to breeds that probably originated in the Middle East.

These close relationships are consistent with the exchange of pigeons along known trade routes between these two regions. Some of this information was actually recorded by a minister and friend of Akbar, who was a tremendous pigeon fancier,” he told Deccan Herald. In the new study, the Utah team along with scientists from Beijing Genomics Institute, University of Denmark and M D Anderson Cancer Centre at the University of Texas mapped the genetic blueprint of the rock pigeon.

They claimed a single mutation in a gene named EphB2 causes head and neck feathers to grow upward instead of downward, creating head crests. It is the first study to pinpoint the linkage between a gene mutation and a pigeon trait, in this case, head crests.

“A head crest is a series of feathers on the back of the head and neck that point up instead of down,” Shapiro says. “Some are small and pointed. Others look like a shell behind the head. They can be as extreme as an Elizabethan collar.”

Charles Darwin was a pigeon afficionado. Not only did he love them, but also relied heavily on the dramatic results of artificial selection in pigeon breeding to communicate his theory on natural selection to the wider audience.

In his ‘Origin of Species’, Darwin noted that pigeon breeds were so distinct that, based on morphology alone, a taxonomist might be tempted to classify them as completely different genera. Yet he also concluded that all breeds were simply variants within a single species, the rock pigeon Columba livia.

More than two centuries later, a group of scientists at the University of Utah decoded the genetic blueprint of this rock pigeon species, unlocking secrets about pigeons’ Middle East origins, feral pigeons’ kinship with escaped racing birds, and how mutations give pigeons traits like a fancy feather hairdo, known as the head crest.
“Birds are a huge part of life on earth, and we know surprisingly little about their genetics,” says Michael Shapiro, one of the two principal authors of the study on the genome sequencing that appeared in February 1 issue of Science. “There are more than 10,000 species of birds, yet we know very little about what makes them so diverse genetically and developmentally.”

Pigeons were probably domesticated in the Mediterranean region at least 3,000–5,000 years ago. Their remarkable diversity can be viewed as the outcome of a massive selection experiment by breeders in Europe. Darwin classified 32 breeds into four groups based on their morphology. They are: the pouters and croppers, which have enlarged crops; wattle breeds many of which have elaborated beaks and large-bodied runts; an artificial grouping diagnosed by a relatively short beak; and breeds that resemble the ancestral rock pigeon. But there are now 350 odd breeds with different sizes, shapes, colours, patterns, beaks, bone structure, vocalisations, flight arrangements and arrangements of feathers on the feet and head, including head crests that come in hoods, manes, shells and peaks.

Earlier studies and pigeon origins

A 2012 study by Shapiro provided limited evidence of pigeons’ origins in the Middle East and some breed origins to India. It also indicated kinship between common feral or free-living city pigeons and escaped racing pigeons.

Modern breeds are frequently described as having origins in England, Germany, Belgium, or elsewhere in Europe, but their progenitors were probably brought there from afar by traders or colonialists.

Most historical accounts trace the origins of the wattle breeds, owls, and tumblers to the Middle and Near East hundreds of years ago, with ancient breeds transported to Europe and India for further development by hybridisation or selection. The genetic analyses are consistent with the common geographic origin.

The fantail breeds probably originated in India and underwent less outcrossing than many other breeds. They show surprising affinity with pouters. These two groups are among the most morphologically extreme of all domestic pigeons, and among the most different from each other. European breeders developed pouters for several hundred years after these birds were brought to Europe from India by Dutch traders.

Historical accounts and genetic similarity between fantails and pouters support the theory of common geographic origin in India. Domestic rock pigeons, on the other hand, were first brought to North America approximately 400 years ago. “Few breeds that are typically associated with India, including the fantails, are genetically very similar to breeds that probably originated in the Middle East.

These close relationships are consistent with the exchange of pigeons along known trade routes between these two regions. Some of this information was actually recorded by a minister and friend of Akbar, who was a tremendous pigeon fancier,” he told Deccan Herald. In the new study, the Utah team along with scientists from Beijing Genomics Institute, University of Denmark and M D Anderson Cancer Centre at the University of Texas mapped the genetic blueprint of the rock pigeon.

They claimed a single mutation in a gene named EphB2 causes head and neck feathers to grow upward instead of downward, creating head crests. It is the first study to pinpoint the linkage between a gene mutation and a pigeon trait, in this case, head crests.

“A head crest is a series of feathers on the back of the head and neck that point up instead of down,” Shapiro says. “Some are small and pointed. Others look like a shell behind the head. They can be as extreme as an Elizabethan collar.”

On-off switch

The EphB2 (Ephrin receptor B2) gene acts as an on-off switch. When mutant, it leads to a crest, but there is no head crest when it is normal. The study went on to illustrate how mutation and related changes in nearby DNA are shared by all crested pigeons, so the trait evolved just once and was spread to numerous pigeon breeds. The researchers ruled out alternate possibility of the genetic mutation arising several times independently in different breeds.

Analysing full or partial genetic sequences for 69 crested birds from 22 breeds, and 95 uncrested birds from 57 breeds, the study established a perfect association between the mutant gene and the presence of head crests. Interestingly, the same gene in humans has been implicated as a contributor to Alzheimer’s disease and prostate cancer. While the head crest trait becomes apparent in juvenile pigeons, the mutant gene affects pigeon embryos by reversing the direction of feather buds – from which feathers later grow – at a molecular level.

“Owl breeds, pigeons with very short beaks and popular with breeders, likely came from the Middle East,” he says. “They are very closely related to breeds we know came from Syria, Lebanon and Egypt.” The study “found a lot of shared genetic heritage between breeds from Iran and breeds we suspect are from India, consistent with historical records of trade routes between those regions. People were not only trading goods along those routes, but probably also interbreeding their pigeons.”

As for the idea that free-living pigeons descended from escaped racing pigeons, Shapiro says his 2012 study was based on “relatively few genetic markers scattered throughout the genome. We now have stronger evidence based on 1.5 million markers, confirming the previous result with much better data.”

The EphB2 (Ephrin receptor B2) gene acts as an on-off switch. When mutant, it leads to a crest, but there is no head crest when it is normal. The study went on to illustrate how mutation and related changes in nearby DNA are shared by all crested pigeons, so the trait evolved just once and was spread to numerous pigeon breeds.

The researchers ruled out alternate possibility of the genetic mutation arising several times independently in different breeds. Analysing full or partial genetic sequences for 69 crested birds from 22 breeds, and 95 uncrested birds from 57 breeds, the study established a perfect association between the mutant gene and the presence of head crests.

Interestingly, the same gene in humans has been implicated as a contributor to Alzheimer’s disease and prostate cancer. While the head crest trait becomes apparent in juvenile pigeons, the mutant gene affects pigeon embryos by reversing the direction of feather buds – from which feathers later grow – at a molecular level.

“Owl breeds, pigeons with very short beaks and popular with breeders, likely came from the Middle East,” he says. “They are very closely related to breeds we know came from Syria, Lebanon and Egypt.” The study “found a lot of shared genetic heritage between breeds from Iran and breeds we suspect are from India, consistent with historical records of trade routes between those regions. People were not only trading goods along those routes, but probably also interbreeding their pigeons.”

As for the idea that free-living pigeons descended from escaped racing pigeons, Shapiro says his 2012 study was based on “relatively few genetic markers scattered throughout the genome. We now have stronger evidence based on 1.5 million markers, confirming the previous result with much better data.”

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